Both are talented Grand Slam champions, but they're also both so prone to mental
collapse that you might get good odds on them ending their careers as one-Slam
wonders.

Especially for Stosur. She's 29 and has slipped to 19th
in the world rankings. Which doesn't mean Grand Slam failure is the only reasonable
expectation for the rest of her career. Slammin' Sammy gets knocked for having
too few tools, but that provides her with more of an out than she deserves. She
is an exceptional athlete, with the second or third best serve and forehand in
the women's game. She's also a skilled volleyer. These are the ingredients to
winning multiple majors. For the next handful of years she will be physically
capable of winning a second major -- especially at Roland Garros, where her
vicious kick serve provides her with a key advantage.

Yet we all know we can't get our hopes up. Since joining the
WTA tour full time in 2003, Stosur has won all of five singles titles -- and
come away with dust 13 times in finals.

Last week in Moscow the Australian beat fellow major
champions Ana Ivanovic and Svetlana Kuznetsova with skill and confidence. She
had plowed through six straight matches without losing a set ... until she fell apart in the final
against 18th-ranked Simona Halep.

Her straight-set loss to journeywoman Francesca Schiavone in the 2010
French Open final is the greatest -- and most unnecessary -- major-final upset
since the 212th-ranked Mark Edmondson beat an out-of-shape and
disinterested John Newcombe at the 1976 Australian Open.

Stosur appears, quite simply, to be emotionally ill-suited
to competition. Expectations weigh on her like bricks. Every cheer from the
gallery breeds a million butterflies in her stomach. This is her nature, and it
always has been, and it's not going to change. Somehow she found herself in a
rare zone in the 2011 U.S. Open final, where she outhit none other than Serena
Williams. We should be happy with that, and encourage her to add to her
impressive doubles C.V., where a partner's presence on court helps keep her
relaxed and focused.

Petra Kvitova is harder to figure out. Every time she puts
it all together -- as she did Tuesday in her match against Agnieszka Radwanska in
the WTA Championships -- we wonder if a new era has begun, the Kvitova
era.

For starters, the 23-year-old Czech left-hander simply looks like a
champion. She has the icy stare of an assassin and the post-hit scream of an
assassin who's so proud of her work she doesn't mind getting caught red-handed.
Even with her little pot belly, she cuts a formidable figure: muscled arms swinging, power braid bobbing, legs that begin somewhere in the upper atmosphere.

She can win as the good cop or the bad cop. In her
breakout year -- like Stosur, in 2011 -- she rolled over Maria Sharapova in the
Wimbledon final, putting the hammer down with a song in her heart. A few months
later, in the final of the WTA Championships, she gutted out a three-set win
over Victoria Azarenka, playing that last set as if her heels were hanging off
the edge of a cliff.

Compared to Stosur, her record in finals is exemplary: 11-4

But that's only because she tends to blow up earlier in
tournaments, not because of nerves -- à
la Stosur
-- but because she navel gazes all the way to her lumbar vertebrae. Her results in the past five major tournaments?
Fourth round, second round, third round, quarterfinals, third round. This from
arguably the second most powerful and talented woman on tour.

Those who love underdogs love Stosur, because, for all her
Ms. Olympia muscles, she has an endearing Charlie Brown quality about her.
They'll be talking about her 2011 major-title run for years to come.

Kvitova, no matter how many early exits she makes in Slams,
will never be thought of as an underdog. She simply has too much of everything that
champions are supposed to have. Can she take control of her perceived status,
more than two full years after her big breakthrough? She'll get a chance later
this week when she takes on Serena Williams. Her career record against the
all-time great: 0-4.